The present invention relates to variable power spectacles whose refractive power is adjustable to supplement accommodation power of eyes.
Japanese Patent Provisional Publication Nos. Sho 55-64209 and Sho 63-24217 disclose the variable power spectacles. The variable power spectacles are provided with a pair of variable power lenses and an adjusting mechanism that adjusts the focal power of the variable power lenses. The variable power lens disclosed in the publications has a flexible hull that is filled by transparent liquid. The adjusting mechanism infuses or discharges the transparent liquid into or from the flexible hull to deform the variable power lens, which changes the curvature of the lens, varying the focal power of the lens continuously.
However, since the variable power lens disclosed in the publications only adjusts the focal power (i.e., focal length), the adjustment disturbs balance between accommodation and vergence of eyes, which becomes a burden on the eye when the spectacles are worn for a long time. Further, the extreme unbalance disables binocular vision.
According to a physiological optics research, it has been understood that accommodation and vergence of eyes should be balanced for good binocular vision and the unbalance disturbs comfortable binocular vision. The vergence means convergence when lines of sights move to inside and means divergence when liens of sights move to outside. FIG. 12 is a graph showing a relationship between the accommodation and the vergence. It has been known that binocular vision is possible only when the relationship between the accommodation and the vergence is represented by a coordinate point included within the area surrounded by a curve 50 in FIG. 12.
However, the adjustment in the conventional variable power spectacles is represented by a straight line 66, for example. If the focal power is adjusted along the line 66, the balance between the accommodation and the vergence is disturbed to disable the binocular vision at the small accommodation.